Film for heat-sensitive mimeograph stencil

ABSTRACT

A film for heat-sensitive mimeograph stencil and a heat-sensitive mimeograph stencil comprising a porous support and the film laminated thereon are disclosed. Since the film of the present invention has an energy of crystal fusion ΔHu of 3-11 cal/g and has a difference Tm in temperature of the crystal fusion-starting point and the crystal fusion-terminating point of 50° C. to 100° C., the heat sensitivity is high, so that the characters and symbols or figures can be printed clearly, and the unevenness in the thickness and the light and shade of the printed characters may substantially be eliminated. Further, since it is not necessary to make the film thin, productivity and ease of handling may be promoted.

TECHNICAL FIELD

This invention relates to a film for heat-sensitive mimeograph stencilwhich may be processed by flash irradiation with a xenon flash lamp andthe like, or by a thermal head. This invention also relates to aheat-sensitive mimeograph stencil employing the film.

BACKGROUND ART

Conventional heat-sensitive mimeograph stencils typically comprise afilm for heat-sensitive mimeograph stencil and a porous support adheredto the film with an adhesive. Conventional films for heat-sensitivemimeograph stencils include vinyl chloride-vinylidene chloride copolymerfilm, polypropylene film and polyethyleneterephthalate film, andconventional porous supports include tissue paper and polyester gauze.

However, if the film for heat-sensitive mimeograph stencil is made of avinyl chloride film, vinylidene chloride copolymer film or apolypropylene film as disclosed in, for example, Japanese PatentDisclosure (Kokai) No. 48395/85, the film does not have sufficientstiffness and its slipperiness is bad, so that a thick film has to beused. Further, since the energy of crystal fusion ΔHu of the resin isgreat, the heat-sensitivity is low. As a result, characters andpaint-printed symbols or figures (symbols or figures such as and inwhich ink is applied in a large area) cannot be printed clearly. On theother hand, if the film for heat-sensitive mimeograph stencil is made ofa polyethyleneterephthalate film as disclosed in, for example, JapanesePatent Disclosure (Kokai) Nos. 85996/85 and 16786/84, the film hassufficient stiffness and the slipperiness is relatively good. However,since its ΔHu is great, to promote heat-sensitivity the thickness of thefilm must be made considerably small. As a result, the film tends to bebroken easily and to be wrinkled during the film forming process, sothat the production yield may be largely reduced. In either case, theshades of the printed characters, and the thicknesses of the printedcharacters are uneven, and the thin black characters cannot be printeddue to the low sensitivity.

DISCLOSURE OF THE INVENTION

Accordingly, the object of the present invention is to provide a filmfor a heat-sensitive mimeograph stencil with a high heat-sensitivity bywhich characters and paint-printed symbols and figures may be clearlyprinted, the characters being free from unevenness of thickness and fromlight and shade, which film excels in durability and ease of handling,and which film offers high production yield.

Another object of the present invention is to provide a heat-sensitivemimeograph stencil employing the above-described film for heat-sensitivemimeograph stencils of the present invention.

The film for heat-sensitive mimeograph stencils of the present inventionis made of a biaxially stretched polyester-based film having an energyof crystal fusion ΔHu of 3-11 cal/g and a difference ΔTm between thecrystal fusion-terminating temperature and the crystal fusion-startingtemperature of 50° C. to 100° C.

The film for heat-sensitive mimeograph stencils of the present inventionhas high heat-sensitivity, so that the printed characters and thepaint-printed symbols and figures are clear and substantially free fromunevenness in thickness and from light and shade. Further, since it isnot necessary to make the film very thin, breaking and wrinkling of thefilm in the production process are unlikely to occur, so that theproduction yield of the film is high. Moreover, the film has excellentdurability, so that the ease of handling of the film is excellent.

BEST MODE FOR CARRYING OUT THE INVENTION

The term "heat-sensitive mimeograph stencil" herein mean those which maybe processed by the well-known method disclosed, e.g., in JapanesePatent Publication (Kokoku) No. 7623/66 using flash irradiation with axenon lamp or using a thermal head, and which comprises a film forforming a heat-sensitive mimeograph stencil (hereinafter referred to as"heat-sensitive film" for short) and a porous support to which theheat-sensitive film is adhered.

As stated above, the heat-sensitive film of the present invention ismade of a polyester-based film. The term "polyester" herein meanspolyester containing as the major acid component an aromaticdicarboxylic acid and as the major glycol component an alkyleneglycol.

Examples of the aromatic dicarboxylic acid may include terephthalicacid, isophthalic acid, naphthalenedicarboxylic acid,diphenoxyethanedicarboxylic acid, diphenyldicarboxylic acid,diphenyletherdicarboxylic acid, diphenylsulfondicarboxylic acid anddiphenylketonedicarboxylic acid. Among these, the most preferred isterephthalic acid.

Examples of the alkyleneglycol may include ethyleneglycol,1,4-butanediol, trimethyleneglycol, tetramethyleneglycol,pentamethyleneglycol and hexamethyleneglycol. Among these, the mostpreferred is ethyleneglycol.

The polyester may preferably be a copolymer. Examples of thecopolymerizable component may include diol components such asdiethyleneglycol, propyleneglycol, neopentylglycol, polyalkyleneglycol,p-xylyleneglycol, 1,4-cyclohexanedimethanol, 5-sodium sulforesorcin;dicarboxylic acid components such as adipic acid, sebacic acid, phthalicacid, isophthalic acid, 2,6-naphthalenedicarboxylic acid and 5-sodiumisophthalic acid; polyfunctional dicarboxylic acid components such astrimellitic acid and pyromellitic acid; and oxycarboxylic acidcomponents such as p-oxyethoxybenzoic acid. The content of such acopolymerizable component in the polyester may preferably be 2-23 mol %,and more preferably 7-18 mol %.

The polyester may contain well-known additives for polyester films suchas antistatic agents and thermal stabilizers in such an amount that theadvantageous properties of the film are not degraded.

The heat-sensitive film of the present invention must be a biaxiallystretched film. Uniaxially stretched film and non-stretched film maygive uneven perforation. Although the degree of biaxial stretching isnot limited, it is usually 2.0-7.0 times, preferably 3.5-6.5 times theoriginal length in both the longitudinal and transvers directions.

The heat-sensitive film of the present invention has an energy ofcrystal fusion ΔHu of 3-11 cal/g, preferably 5-10 cal/g. If the ΔHu isless than 3 cal/g, the heat-sensitive film may stick to the originalcopy (manuscript) and clear characters may not be printed. If the ΔHu ismore than 11 cal/g, paint-printing characteristics, sensitivity and theexpression of light and shade may be degraded. It should be noted thatif the ΔHu is not more than 10 cal/g, the perforation time may beshortened so that productivity may be promoted.

In the heat-sensitive film of the present invention, the difference inthe temperature ΔTm between the fusion terminating point and the fusionstarting point is 50° C. to 100° C., and preferably 60° C. to 90° C. Ifthe ΔTm is less than 50° C., the paint-printing is unclear and has lightand shade, so that the object of the present invention cannot beattained. On the other hand, if the ΔTm is more than 100° C., thethickness of the printed characters is uneven. It should be noted thatif the ΔTm is less than 90° C., the dimensional change of thepaint-printed symbols or figures from those in the original copy may bereduced.

In a preferred mode of the present invention, the center line averageroughness (Ra) is 0.05-0.3 μm, more preferably 0.09-0.25 μm. If thecenter line roughness is in the above-mentioned range, winding the filmin the production process may be satisfactorily conducted without makingfolded wrinkles and the transparency of the film is excellent, so thatthe sensitivity of the film may be further improved.

Further, in a preferred mode of the present invention, theheat-sensitive film has a maximum roughness (Rt) of 0.5-4.0 μm, morepreferably 0.8-3.5 μm. If the maximum roughness is in this range, thewinding characteristic of the film in the production process is good andthe film is hardly broken in the production process.

Further, in view of the preferred slipperiness, transparency andsensitivity, the heat-sensitive film of the present invention preferablyhas 2,000 to 10,000 projections, more preferably 2,500 to 8,000projections per 1 mm².

Still further, in view of the preferred slipperiness, windingcharacteristic and productivity, the heat-sensitive film of the presentinvention preferably has 20 to 1,000, more preferably 50 to 800projections per 1 mm², which projections have a diameter of 8-20 μm.

The above-mentioned specific surface configuration, that is, thespecific roughness and the projection density may be obtained byblending in the film particles made of an oxide or an inorganic salt ofan element belonging to any of the IIA group, IIIB group, IVA group orIVB group in the periodic table by the method hereinafter described.Examples of the materials constituting the particles may includesynthesized and naturally occurring calcium carbonate, wet silica(silicon dioxide), dry silica (silicon dioxide), aluminum silicate(kaolinite), barium sulfate, calcium phosphate, talc, titanium dioxide,aluminum oxide, aluminum hydroxide, calcium silicate, lithium fluoride,calcium fluoride and barium sulfate. Among these, those inorganicparticles with a Mohs' hardness of 2.5 to 8 are especially preferredbecause the plating characteristics may be improved. Examples of suchparticles include calcium carbonate, titanium dioxide, silica, lithiumfluoride, calcium fluoride and barium sulfate. These inactive particlespreferably have an average particle size of 0.1-3 μm. It is especiallypreferred that the particles have an average particle size of 0.5-2.5times the film thickness because the plating characteristics may befurther improved. Although the content of the inactive particles variesdepending on the material of the particles and the particle size, asusual, it is preferably 0.05-2.0% by weight, more preferably 0.1-1.0% byweight for forming the above-described specific surface configuration.In a preferred mode of the present invention, the heat-sensitive film ofthe present invention contains therein at least one higher aliphaticsubstance of which a major component is a C₁₀ -C₃₃, more preferably aC₂₀ -C₃₂ higher aliphatic monocarboxylic acid or an ester thereof. Byincorporating such a substance in the film, the printing sensitivity andthe expression of light and shade may further be improved.

Preferred examples of the C₁₀ -C₃₃ higher aliphatic monocarboxylic acidmay include capric acid, lauric acid, stearic acid, nonadecanoic acid,arachic acid, behenic acid, melissic acid, lignoceric acid, cetolicacid, montanic acid, hentriacontanoic acid, petroselinic acid, oleicacid, erucic acid, linoleic acid and mixtures thereof.

The term "higher aliphatic monocarboxylic acid ester" herein means thoseobtained by esterifying the whole or a part of the carboxylic group ofthe above-mentioned higher aliphatic monocarboxylic acid with amonovalent or divalent C₂ -C₃₃, preferably C₁₈ -C₃₃, more preferably C₂₀-C₃₂ aliphatic alcohol. Preferred examples of the higher aliphaticmonocarboxylic acid ester may include montanic acid ethyleneglycolester, ethyl montanate, ceryl montanate, octacosyl lignocerate, myricylcerotate and ceryl cerotate, as well as naturally occurring montanicwax, carnauba wax, beads wax, candelilla wax, bran wax and insect wax.

The term "major component" herein means the component is contained inthe amount of 50% by weight or more.

The content of the higher aliphatic substance in the film may preferablybe 0.005-5% by weight, more preferably 0.01-3% by weight based on theweight of the polyester.

The heat-sensitive film of the present invention preferably has athickness of 0.2-10 μm, more preferably 0.3-7 μm. If the thickness ofthe film is in this range, wrinkles are hardly made in winding, adhesionwith the porous support is easy and the pirinting durability is high.

It is preferred that the total of the heat shrinkage in the longitudinaland transverse directions of the film at 150° C. be 6-33%, morepreferably 10-24%. In this case, it is preferred that the ratio of theheat shrinkage in the transverse direction to that in the longitudinaldirection be 0.75 to 1.25 for preferred processing characteristics.

Further, it is preferred that the total of the thermal stress in thelongitudinal and transverse directions at 80° C. and 90° C. be 0-200g/mm² and 250-1,000 g/mm², respectively for preferred processingcharacteristics.

The heat-sensitive film of the present invention may be produced by thefollowing process. The above-described polyester or polyester copolymeror a mixture thereof, which contains, if necessary, the above-describedspecific inorganic particles and/or higher aliphatic substance issupplied to an extruder, and molten polymer may then be extruded througha T-die, and cast onto the cooling drum. The obtained film is thenbiaxially stretched to obtain the heat-sensitive film of the presentinvention. The biaxial stretching is, although not restricted, usuallyconducted under a temperature between the glass transition temperature(hereinafter referred to as "Tg") of the film and Tg+50° C., at astretching ratio of 2.0-7.0 times the original dimension in both thelongitudinal and transverse directions. More preferably, the film may bestretched in the longitudinal direction at a stretching ratio of 3.5-6.5 times the original length at a temperature of 90° C. to 115° C. andthen stretched in the transverse direction at a temperature of 90° C. to120° C. The method of biaxial stretching is not restricted andsuccessive biaxial stretching and simultaneous stretching (stentermethod or tube method) may be employed. The thus obtained film may beheated at a temperature between (melting point -10° C.) to (meltingpoint -120° C.) with 0-20% relaxation. For preferred processingcharacteristics, it is most preferred to heat the film at 110° C. to180° C. with 0-9% relaxation.

In cases where the above-mentioned inorganic particles are incorporatedin the film in order to obtain the above-described specific surfaceconfiguration, it is preferred to prepare a master polymer comprisingthe inorganic particles in a polyester or a polyester copolymer and toadmix the master polymer with the polyester or the polyester copolymerwhich is the major component of the film, since the processingcharacteristics may be further improved. In this case, it is preferredto employ as the master polymer a polyester or a polyester copolymerwhich has a melting point of 10° C. to 100° C. higher than that of themajor component polymer and/or which has an intrinsic viscosity (IV) of0.2 to 1.0 higher than that of the major component polymer, and whichhas some compatibility with the major component polymer for obtainingthe specific surface configuration. Needless to say, the surfaceconfiguration may be controlled to some degree by controlling theshearing stress exerted in the extrusion step, weight per unit area ofthe filter, or extrusion conditions.

The heat-sensitive mimeograph stencil of the present invention may beobtained by laminating and adhering the heat-sensitive film of thepresent invention on a porous support. Representative examples of theporous support include porous tissue paper, tengjo paper, syntheticfiber paper, various woven fabrics and non-woven fabrics. Although theweight per unit area of the porous support is not restricted, it isusually 2-20 g/m², preferably 5-1.5 g/m². In cases where a mesh sheet isused as the porous support, those mesh sheets which are woven withfibers having a diameter of 20-60 μm, and which have a lattice intervalof 20-250 μm may preferably be employed for preferred printingcharacteristics.

Representative examples of the adhesive used for adhering theheat-sensitive film and the porous support include vinyl acetate-basedresins, acrylic resins, urethane-based resins and polyester-basedresins.

In a preferred mode of the heat-sensitive mimeograph stencil of thepresent invention, a non hot-sticking layer is formed on the surface ofthe heat-sensitive film which surface is opposite to the surfacecontacted with the porous support. The non hot-sticking layer is formedin order to prevent the heat-sensitive film from sticking to theoriginal copy in case of processing by flash irradiation or to a thermalhead in case of processing with the thermal head. Since the sticking ofthe heat-sensitive film with the thermal head is severe, theheat-sensitive mimeograph stencil which is to be processed with thethermal head is especially preferred to have the non hot-sticking layer.

The non hot-sticking layer may be made of a thermosetting or anon-fusible substance, which is not fused by heating at all. Examples ofsuch a substance include thermosetting silicone resins, epoxy resins,melamine resins, phenol resins, thermosetting acrylic resins andpolyimide resins.

As the material constituting the non hot-sticking layer, thosesubstances which are liquefied at room temperature or under heat toprevent the sticking, such as metal salts of fatty acids, polysiloxaneand fluorine oil may preferably be employed. Among these, thosesubstances which are solid at room temperature and are liquefied underheat, which, upon cooling to a temperature lower than the melting point,remain as liquid are especially preferred. Examples of such a substanceinclude dicyclohexyl phthalate, diphenyl phthalate, triphenyl phosphate,dimethyl fumarate, benzotriazole, 2,4-dihydroxybenzophenone,tribenzylamine, benzil, phthalophenone, p-toluensulfonamide andpolyethyleneglycol.

The non hot-sticking layer may also preferably be made of a substanceexcelling in releasing properties. Examples of such a substance includefluorine-contained polymers, silicone resins, perfluoroacrylic resins,vinyl chloride resins and vinylidene chloride resins.

Further, for preferred adhesiveness with the polyester resin and oftranscription to the reverse side when stored in rolled state, alsopreferred are a non hot-sticking layer consisting essentially of amixture of (A) crosslinked polyester copolymer and (B)organopolysiloxane, which has a (B)/(A) weight ratio of 0.01 to 8, and anon hot-sticking layer containing not less than 10% by weight of curedsubstance consisting essentially of an urethane prepolymer (A) havingorganopolysiloxane as its principal chain, which has a free isocyanategroup as a terminal group and/or pendant group. Especially preferred nonhot-sticking layer consists essentially of a cured substance containingan urethane prepolymer (A) having organopolysiloxane as its principalchain, which has a free isocyanate group as a terminal group and/orpendant group and a polymer (B) having an active hydrogen atom, theweight ratio of (A)/(B) being 10/90 to 90/10. These non hot-stickinglayers will now be described in more detail.

In the non hot-sticking layer containing not less than 10% by weight ofcured substance consisting essentially of an urethane prepolymer (A)having organopolysiloxane as its principal chain, which has a freeisocyanate group as a terminal group and/or pendant group, theprepolymer (A) may be synthesized by blending the compound representedby the following formula (1) or (2) with an organic isocyanate in excessamount with respect to the number of the active hydrogens in thecompound (1) or (2): ##STR1## (wherein R¹ -R⁴, the same or different,represent methyl group or phenyl group; R⁵ represents oxyalkylene group,polyoxyalkylene group or mercapto group; X represents hydroxide group;and m and n, the same or different, represent an integer of 3-200). Asthe organic polyisocyanate, known aromatic, alicyclic or aliphaticpolyisocyanates may be used. Glycols, polyols and water may be used as achain elongating agent.

The synthesized urethane prepolymer (A) has free isocyanate group ofwhich content is 1-10% by weight, preferably 1-7% by weight. Since thefree isocyanate group is very reactive, those prepolymers of whichisocyanate group is blocked by a blocking agent may preferably be used.The blocked urethane prepolymer (A) may stably be dispersed in water.Examples of the blocking agent include ethyleneimine, lactams, oximes,phenols and hydrogensulfite and these blocking agents may preferably beselected depending on the heat-curing conditions. In usual, thoseblocking agents which dissociate at 100° C.-180° C. are preferred. Inthis case, upon heating, the blocking agent dissociates to cross-linkand cure the urethane prepolymer (A), so that the urethane prepolymer(A) can accomplish its role as a non hot-sticking layer. Morepreferably, the urethane prepolymer (A) is mixed with a polymer (B)having active hydrogen atoms to promote the adhesivity with theheat-sensitive film and to prevent the transcription of the hot-stickinglayer to the reverse side.

The polymer (B) having active hydrogen atoms may be any polymer whichcontains active hydrogen atoms in the polymer molecule. Examples of thegroup containing the active hydrogen atom include hydroxide group, aminogroup and mercapto group, and examples of the polymer containing such agroup include polyester resins, polyamide resins, polyesterether resins,polyesteramide resins, polyetheramide resins, polyvinylalcohol resins,epoxy resins, melamine resins, urea resins, celluloses, methylols, aswell as acrylic resins, phenol resins, silicone resins, polyurethaneresins, which contain amino group, hydroxide group or carboxyl group,and modified resins thereof.

It is preferred that the urethane prepolymer (A) be contained in the nonhot-sticking layer in the amount of not less than 10% by weight. Asstated above, by blending a polymer (B) with the prepolymer (A),advantageous effects may be brought about. In this case, the mixingratio of the prepolymer (A) to polymer (B) by weight may preferably be10/90 to 90/10, more preferably 20/80 to 80/20 for further promoting theadhesiveness with the heat-sensitive film and the prevention of thetranscription to the reverse side.

In the mixture of the prepolymer (A) and the polymer (B), varioussurface active agents may be incorporated in an amount not to degradethe properties of the non hot-sticking layer, and heat-resisting agents,weather-resisting agents, coloring agents, lubricants and the like mayalso be incorporated. Further, to enhance the dissociation of theblocking agent from the blocked isocyanate, a basic compound may beincorporated to adjust the pH. To promote the reactivity of the freeisocyanate, a known catalyst such as dibutylstannicdilaurate may also beadded.

In cases where the non hot-sticking layer is made of a mixture ofcross-linked polyester copolymer (A) and organopolysiloxane (B), thecross-linked polyester copolymer (A) may be those obtained by blending apolyester with a known cross-linking agent which reacts with a carboxylgroup or hydroxide group at the terminal of the polyester to cross-linkthe polyester and then heating or irradiating the polyester with anultraviolet beam or electron beam. Alternatively, the cross-linkedpolyester copolymer may be one obtained by introducing a reactive groupinto the polyester copolymer and then self-cross-linking the polyestercopolymer with or without using. a cross-linking agent.

The polyester copolymer which is to be cross-linked may be any polyestercopolymer containing a carboxyl group or hydroxide group, which isobtained by polycondensing a dicarboxylic acid component and a glycolcomponent.

The dicarboxylic acid component may be an aromatic, aliphatic andalicyclic dicarboxylic acid and examples of the carboxylic acidcomponent may include terephthalic acid, isophthalic acid,ortho-phthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid,sebacic acid, succinic acid, glutaric acid, 1,3-cyclopentanedicarboxylicacid, 1,3-cyclohexanedicarboxylic acid, dodecanedicarboxylic acid andazelaic acid. Further, a sulfonic acid metal salt-containingdicarboxylic acid may be employed as a copolymerization component inorder to give water-solubility or water-dispersibility to the polyestercopolymer. Examples of the sulfonic acid metal salt-containingdicarboxylic acid include metal salts of sulfoterephthalic acid,4-sulfonaphthalene, 2,7-dicarboxylic acid and5[4-sulfophenoxy]isophthalic acid.

The glycol component which is to be reacted with the dicarboxylic acidmay be a C₂ -C₈ aliphatic glycol or a C₆ -C₁₂ alicyclic glycol. Examplesof the glycols may include ethyleneglycol, 1,2-propyleneglycol,1,3-propanediol, 1,4-butanediol, neopentylglycol, 1,6-hexanediol,1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, p-xylyleneglycol,diethyleneglycol and triethyleneglycol. As a part of the glycolcomponent, polyethyleneglycol or polytetramethyleneglycol may beemployed.

The polyester copolymer obtained from the above-mentioned dicarboxylicacid component and the glycol component may be used in the form ofsolution or dispersion in water, in an organic solvent, or in a mixtureof water and an organic solvent.

The polyester copolymer preferably has a number of terminal groups forpreferred cross-linking property, and those having a hydroxide value of3-200 mg KOH/g polymer, especially 5-100 mg KOH/g polymer are preferredin view of the reactivity and the stiffness of the coated film. Thepolyester copolymer preferably has a glass transition point of 10° C. to90° C., more preferably 40° C. to 70° C. for preferred anti-stickingproperty.

As to the cross-linking agent for cross-linking the polyester copolymer,this may be any one which reacts with the terminal carboxyl group orhydroxide group. Representative examples of the cross-linking agent mayinclude urea type, melamine type and acrylamide type polymer orprepolymer containing methylol or alkylol group, epoxy compounds,isocyanate compounds and aziridine compounds. Among these, for preferredadhesiveness with the heat-sensitive film and the non hot-stickingproperty, methylolmelamine and isocyanate compounds are preferred.Although the amount of the cross-linking agent added may appropriatelybe selected depending on the nature of the employed cross-linking agent,it is usually preferred to add equivalent cross-linking agent withrespect to the terminal groups. Usually, the cross-linking agent maypreferably be used in the amount of 2 to 30 parts, more preferably 5 to20 parts by weight with respect to 100 parts by weight of the polyestercopolymer in terms of solid contents.

The polyester copolymer in which a reactive group is introduced is onein which the following compounds having a functional group such asreactive group, self-cross-linking group and hydrophilic group isintroduced into the stem polymer. Examples of the compounds containingcarboxyl group, its salt or acid anhydride group may include acrylicacid, methacrylic acid, itaconic acid, maleic acid, fumaric acid andcrotonic acid. Examples of the compounds containing amide group ormethylolated amide group may include acrylamide, methacrylamide,N-methylmethacrylamide, methylolacrylamide, methylolated methacrylicamide, ureidovinyl ether, β-ureidoisobutylvinyl ether andureidoethylacrylate. Examples of the compounds containing hydroxidegroup may include β-hydroxyethylmethacrylate, β-hydroxypropylacrylate,β-hydroxypropylmethacrylate, β-hydroxyvinyl ether, 5-hydroxypentylvinylether, 6-hydroxyhexylvinyl ether, polyethyleneglycolmonoacrylate,polyethyleneglycolmonomethacrylate, polypropyleneglycolmonoacrylate andpolypropyleleglycolmonomethacrylate. Examples of compounds containingepoxy group may include glycidylacrylate and glycidylmethacrylate.

Among these compounds containing a reactive group, for preferredadhesiveness with the heat-sensitive film and anti-sticking property,acrylic acid and grafted compound of the methylolated acrylamide areespecially preferred.

Although the polyester copolymer containing the reactive group may becross-linked by heating or the like after coating, it is preferred toemploy a cross-linking catalyst for enhancing the cross-linkingreaction. Examples of the cross-linking catalyst may include ammoniumchloride, ammonium nitrate, citric acid, oxalic acid, p-toluenesulfonicacid and dialkylzinc complex. The amount of the cross-linking catalystmay be 0.5-5 parts by weight, preferably 1-3 parts by weight withrespect to 100 parts by weight of the polyester copolymer in terms ofsolid contents.

As the above-mentioned organopolysiloxane (B) employed along with thecross-linked polyester copolymer may be silicone oils and modifiedsilicone oils in which various functional groups are introduced for thepurpose of conferring compatibility with the resin to be blended,hydrophilicity, reactivity, adsorbing ability, lubricating ability andso on. Representative examples of the organopolysiloxanes to be employedmay include those represented by the following formulae (3) to (5).##STR2## (wherein x, y and z, the same or different, represent aninteger of 1 to 5,000; R represents C₁ -C₁₀₀ alkyl group or hydroxidegroup; R' represents C₁ -C₁₀ alkylene group, phenylene group,cyclohexylene group or ether group; R" represents hydrogen, C₁ -C₁₀₀alkyl group, epoxy group, amino group, carboxyl group, phenyl group,hydroxide group, mercapto group, polyoxylenealkyl group orhalogen-containing alkyl group; R"'represents C₁ -C₁₀₀ alkyl group,polyoxylenealkyl group, hydroxide group or halogen-containing alkylgroup).

Preferred examples of the organopolysiloxanes represented by theformulae (3) to (5) may include dimethylpolysiloxane oils,amino-modified silicone oils, epoxy-modified silicone oils,epoxy-polyether-modified silicone oils, epoxypolyether-modified siliconeoils, carboxyl-modified silicone oils, polyether-modified silicone oils,alcohol-modified silicone oils, alkyl- or alkyl-aralkyl-modifiedsilicone oils, alkylaralkyl-polyether-modified silicone oils,fluorine-modified silicone oils, alkyl-higher alcohol ester-modifiedsilicone oils, methylhydrogenpolysiloxane oils, phenylmethylsiliconesand emulsions thereof.

Among these, in view of the anti-sticking property and noise preventionproperty, dimethylpolysiloxane oils, epoxy-modified silicone oils,epoxy-polyether-modified silicone oils, polyether-modified silicone oilsand amino-modified silicone oils, as well as the emulsion thereof arepreferred. Mixtures of two or more of these with any mixing ratio may beemployed. Further, known cross-linking agents which react with thereactive groups of the silicone oil may also be used.

For example, it is preferred to use a compound such as amine, amide andmelamine along with the silicone oil having an epoxy group since theelimination of the oil may be reduced.

The organopolysiloxanes suitable for employing in the non hot-stickinglayer have a viscosity of 100-5,000,000 centistokes, more preferably2,000-3,000,000 centistokes at 25° C.

Although cross-linkable polyester copolymer (A) and theorganopolysiloxane (B) may be admixed in any mixing ratio using a commonorganic solvent or water the mixing ratio (B)/(A) by weight maypreferably be 0.01-8, more preferably 0.05-3, still more preferably0.1-0.7.

Although the thickness of the non hot-sticking layer is not restricted,it may preferably be 0.01-1 μm, more preferably 0.05-0.5 μm.

For adhesiveness with the heat-sensitive film and for prevention of thetranscription to the reverse side, the non hot-sticking layer may beformed by applying a solution of the compounds on the heat-sensitivefilm, stretching the heat-sensitive film while drying the appliedsolution and then heatsetting the resulting film.

Methods and various characteristics relating to the present inventionand methods of evaluating the effects of the present invention will nowbe described in summary.

(1) Energy of Crystal Fusion [ΔHu (cal/g)]

The energy of crystal fusion was obtained from the area (a) of a regionin the thermogram of the heat-sensitive film while the fusion takesplace, using a differential scanning thermometer type DSC-2 manufacturedby Perkin-Elmer Co., Ltd. The region was that interposed between thebase line of the thermogram and the differential thermal curve in therange from the fusion-starting temperature to the fusion-terminatingtemperature. That is, the differential thermal curve deviates from thebase line to the endothermic side as the heating continues and thenreturns to the base line. The area (a) is that of the region interposedbetween the deviated differential thermal curve and the straight lineconnecting the point at which the deviation of the differential thermalcurve begins and the point at which the deviated curve returns to thebase line. The same procedure was followed for indium to obtain thecorresponding area (b) which is known as 6.8 cal/g. The energy of fusionwas obtained by the following equation: a/b×6.8=ΔHu (cal/g)

(2) Difference Between the Fusion-Starting Temperature andFusion-Terminating Temperature ΔTm (°C.)]

Using the differential scanning thermometer type DSC-2 as in (1), thetemperature at which the differential thermal curve begins to deviatefrom the base line was defined as the fusion-starting temperature (T₁)and the temperature at which the deviated differential thermal curvereturns to the base line was defined as fusion-terminating temperature(T₂), and the ΔTm was obtained by the equation T₂ -T₁ =ΔTm (°C.). Incases where the position of the each base line is difficult to clearlydefine, tangent line was drawn for each base line and the points atwhich the differential thermal curve starts to deviate, and returns toeach tangent line were read. In cases where ΔHu =0 cal/g, ΔTm is definedas ∞.

(3) Evaluation of Character Printing

(i) Evaluation of Clearness of Characters

The original copy (manuscript) carried JIS first level characters in thesize of 2.0 mm square. Mimeograph stencil comprising a porous supportmade of polyester gauze and a heat-sensitive film adhered thereto wasprocessed using a mimeographing printer "RISO Meishigokko" (manufacturedby Riso Kagaku Kogyo K.K.) and the printed characters were evaluated. Bythe evaluation, the mimeograph stencils were classified into threeranks. The A rank mimeograph stencils are those by which characters wereprinted as clear as the original copy. The B rank stencils are thosewhich gave characters whose lines, unlike the original copy, were cutand/or combined although which characters could be read. The C rankstencils are those which gave characters of which the lines were cutand/or combined such that the characters could not be read

(ii) Evaluation of Chipping of Characters

Processing and printing were conducted as in (i) just described above,and the chipping of the characters were evaluated. Those mimeographstencils which gave characters clearly chipping were evaluatedunacceptable and are expressed by the mark "X" in the tables. Thosewhich gave characters which did not chip at all were evaluated asacceptable and are expressed by the mark "◯" in the tables. Those whichgave characters slightly chipping but could be read are expressed by themark "Δ".

(iii) Evaluation of Unevenness of Thickness of Character Lines

By the same manner as in (i), characters with a size of 5.0 mm squarewere printed, and the printed characters were subjected to visualexamination.

Those mimeograph stencils by which characters clearly showing unevennessof the lines thereof when compared with the original copy (manuscript)were printed were evaluated as giving bad appearance and unacceptable,and are expressed by the mark "X". Those which gave characters notshowing unevenness of the lines thereof were evaluated as giving goodappearance and acceptable, and are expressed by the mark "◯".

(iv) Evaluation of Thickness of Lines of Characters

Characters were printed in the same manner as in (iii), the change inthe thickness of the lines of the characters from the original copy werevisually examined. Those mimeograph stencils by which characters whoselines were thickened or thinned when compared to the original copy wereprinted were evaluated as unacceptable and are expressed by the mark"X". Those which gave characters of which lines did not change in thethickness are expressed by the mark "◯". Those characters of which lineswere slightly thickened or thinned but in an acceptable level areexpressed by the mark "Δ".

(4) Evaluation of Paint-Printing

(i) Evaluation of Clearness of Paint-Printing

(circles painted in black) with a diameter of 1-5 mm were printed in thesame manner as described above. The printed circles were subjected toevaluation.

The evaluation was made for the ruggedness of the boundaries of thecircles. Those mimeograph stencils which gave circles whose boundarieshave a portion which projects or recesses by 200 μm or more with respectto the size of the original copy were evaluated as giving bad appearanceand unclear printing, and are expressed by the mark "X". Those whichgave circles having a projection or a recess of 50 μm or smaller wereevaluated as being clear and are expressed by the mark "◯". Those whichwere intermediate therebetween are expressed by the mark "Δ". These canbe acceptable for some use.

(ii) Correspondence of the Size of Original Copy and Paint-Printed Copy

Circles painted in black were printed as in (i), and the diameters ofthe painted circles in various directions (i.e., 0° and 180°, 45° and225°, 90° and 270°, and 135° and 315°) were measured. Those which gaveprinted circles showing a dimensional change from the original copy(larger or smaller) by not less than 500 μm were evaluated as giving badcorrespondence and are expressed by the mark "X". Those which gaveprinted circles which showed a dimensional change of not more than 50 μmwere evaluated as giving good correspondence and are expressed by themark "◯". Those which were intermediate therebetween are expressed bythe mark "Δ". These can be acceptable for some use.

(iii) Evaluation of Light and Shade Shown in Paint-Printing

Paint-printing was conducted as in (i), and the printed circles werevisually checked whether they have light and shade or not. Thosemimeograph stencils which gave printed circles showing light and shadeare expressed by the mark "X" and those not showing light and shade areexpressed by the mark "◯".

Evaluation of Sensitivity

Characters were written with pencils having a pencil hardness of 5H, 4H,3H, 2H and H at a pressing force of 150 g and were used as a manuscript.The sensitivity was evaluated whether the printed characters were ableto be read. Since the character written with a pencil of 5H was thelightest and the character written with a pencil of H was the deepest,the sensitivity was the highest if the printed character of whichmanuscript was written with a pencil of 5H could be read and thesensitivity decreases as the highest pencil hardness by which readableprinted character could be made shifts from 5H to H.

(6) Evaluation of Durability

The durability was expressed in terms of the number of prints (known aswithstand printing number) which could be printed until theheat-sensitive film was broken using the above-mentioned printer.

(7) Center Line Average Roughness (Ra)

The center line average roughness (Ra) was measured in accordance withthe method of JIS B 0601 using a pin-touch type surface roughness meter.The cutoff was 0.25 mm and the measuring length was 4 mm.

(8) Maximum Roughness (Rt)

The maximum roughness was measured using a pin-touch type surfaceroughness meter in accordance with the method of JIS B 0601. The maximumroughness means the total of the height of the highest mountain and thedepth of the deepest valley wherein the measuring length was 4 mm.

(9) Diameter and Number of Projections

Aluminum was vapor-deposited with a thickness of about 100 nm on thefilms to prepare film samples for observation. Using a microscope(reflection method) and an image analyzing computer (CambridgeInstrument Co., Ltd.), the samples were magnified to 358 magnificationsand were provided with contrast, and the size (diameters) and the numberof the projections were measured. The area occupied by the projectionwas calculated in terms of area of a circle, and the size of theprojections were expressed in terms of the diameter of the circle.

(10) Average Particle Size

Slurry of the inorganic particles in ethanol was prepared and theaverage particle size was determined using a centrifugal sedimentationtype particle size distribution-measuring apparatus CAPA-500(manufactured by Horiba Seisakusho).

(11) Stretching Property

Evaluation was made for whether the film is broken or not by beingstretched in transverse direction in a stenter. Those films which werebroken within 8 hours were evaluated as having bad stretching propertyand were expressed by the mark "X". Those films which was not brokenwithin 72 hours were evaluated as having good stretching property andwere expressed by the mark "◯". Those films which were broken at thetime of 8 hours to 72 hours from the beginning of the stretching wereevaluated as being practically acceptable although the productivitywould be lowered, and were expressed by the mark "Δ".

(12) Winding Property

The conditions of the films when they were wound about a winder werevisually examined. The criteria of the evaluation were as follows: Mark⊚: Those films which did not show folded wrinkles, longitudinal wrinkleswhich did not reach to folded wrinkles, transverse wrinkles which didnot reach to folded wrinkles and side slips (0.5 mm or less) at all wereevaluated as having good winding property and were expressed by the mark"⊚". Mark ◯: Those films which showed longitudinal and/or transversewrinkles which did not reach to folded wrinkles, but which did not bringabout troubles in rewinding step and in adhering step, as well as thosewhich showed a side slip of 1.0 mm or less were evaluated as beingpractically usable and were expressed by the mark "◯". Mark X: Thosefilms which showed folded wrinkles and which showed longitudinal and/ortransverse wrinkles not reaching to folded wrinkles but brought abouttroubles in rewinding step and in adhering step, as well as those whichshowed a side slip of more than 1.0 mm were evaluated as beingpractically unusable and were marked as "X".

(13) Heat Shrinkage

Films were cut into 1 cm width×30 cm length to prepare film samples. Thepoint at 5 cm from the edge of the sample was marked and the point at 20cm from the mark was also marked. Three grams of load was applied to theedge of the sample and the sample was heat-treated at 150° C. for 15minutes in "Perfect Oven" manufactured by Tahai Co., Ltd. After theheat-treatment (HT), the distance between the marks was measured. Theheat shrinkage (HS) was obtained from the following equation: ##EQU1##

(14) Adhesiveness

The adhesiveness between a polyester gauze used as the porous supportand the heat-sensitive film was evaluated. Cellophane tapes were adheredto the surfaces of the polyester gauze and the heat-sensitive film,respectively, and the cellophane tapes were pulled off. Those from whichthe polyester gauze was completely pulled off were evaluated as havingpoor adhesiveness and were expressed by the mark "X", and those fromwhich the polyester gauze was not pulled off at all were evaluated ashaving good adhesiveness and were expressed by the mark "◯". Those inwhich the polyester gauze was partly pulled off were expressed by themark "Δ".

(15) Releasing Property

Ease of detaching the manuscript from the heat-sensitive mimeographstencil after processing was evaluated. Those from which the manuscriptcould be detached without any resistance were evaluated as having goodreleasing property and were expressed by the mark "◯". Those to whichthe manuscript was kept attached but from which the manuscript could bedetached without leaving any deffect on the processed region wereevaluated, although the ease of handling was reduced as practicallyusable and were expressed by the mark "Δ". Those in which a deffect isleft on the processed region when detaching the manuscript therefrom, aswell as those in which the heat-sensitive film was broken were evaluatedas unusable and were expressed by the mark "X".

(16) Evaluation of Anti-Curling Property

The heat-sensitive mimeograph stencils after being processed with theabove-mentioned printer were evaluated. The mimeograph stencils afterprocessing were cut into 5 cm×8 cm, and the thus cut stencils wereplaced on a flat desk with facing the heat-sensitive film upside. Thosewhich did not curl at all were evaluated as having good anti-curlingproperty and were expressed by the mark "◯". Those which were lifted by10 mm or more were evaluated as having poor anti-curling property andwere expressed by the mark "X". Those intermediate therebetween wereexpressed by the mark "Δ".

(17) Evaluation of Anti-Sticking Property

Using Risograph 007D III N with a thermal head, reading of a manuscriptand perforative writing and printing were conducted. Those which did nowshow sticking at all during the operation were evaluated as having goodanti-sticking property and were expressed by the mark "⊚". Those whichshowed slight sticking but did not have a practical problem wereexpressed by the mark "◯", and those which showed sticking are expressedby the mark "X".

(18) Evaluation of Noise

Perforation operation was conducted as in (17) and the noise made in theoperation was evaluated. Those which made noise are expressed by themark "X", and those which did not make noise are expressed by the mark"◯".

(19) Surface Wetting Tension

To evaluate the transcription of the non hot-sticking layer to thereverse surface, a non hot-sticking layer was superposed on a bareheat-sensitive film and a pressure of 100 g/cm² was applied thereto. Thethus superposed structure was left to stand at a temperature of 40° C.,and a relative humidity of 95% for two days. Thereafter the conditionsof the non hot-sticking layer and the surface of the film contacted withthe non hot-sticking layer were evaluated in accordance with the methodof JIS K 6768. In cases where the transcription of the non hot-stickinglayer to the surface of the heat-sensitive film does not occur orscarecely occurs, the surface wetting tension of the heat-sensitive filmis assumed to be 38-43 dynes/cm. Thus, in cases where the surfacewetting tension was not more than 37 dynes/cm, it is evaluated that thetranscription of the non hot-sticking layer to the reverse side of thefilm when rolled is severe.

The present invention will now be described by way of examples andcomparative examples thereof. The examples are presented for theillustration purpose only and should not be interpreted any restrictiveway.

COMPARATIVE EXAMPLE 1

Polyethyleneterephthalate resin with an intrinsic viscosity (IV) of 0.6was supplied to an extruder and was melt-extruded through a T-die at280° C. The molten resin was cast onto a cooling drum with a temperatureof 70° C. to form a cast film. The film was stretched to 4.5 times theoriginal length at 90° C. in the longitudinal direction. The film wasthen stretched to three times the original length at 100° C. intransverse direction. The film was subsequently heatset under restraintin the stenter at 210° C. for 5 seconds to obtain a biaxially stretchedfilm having the thickness of 2.0 μm.

The ΔHu and ΔTm of the thus obtained heat-sensitive film were measured.Further, the thus obtained heat-sensitive film was laminated on, andadhered to a polyester gauze and was subjected to printing using theprinter, and character printing characteristics, paint-printingcharacteristics, sensitivity and withstand printing number wereevaluated as mentioned above. The results are shown in Table 1.

EXAMPLES 1-5, COMPARATIVE EXAMPLE 2

The same procedure as in Comparative Example 1 was repeated except thatthe material used was ethyleneterephthalate-isophthalate copolymer. Thecontent of the isophthalate of Examples 1-5 and Comparative Example 2was 2.5, 5.0, 10, 15, 20 and 25% by weight, respectively. The thicknessof the film was 2.0 μm. In Examples 4 and 5 and in Comparative Example2, the temperature during the stretching in the longitudinal directionwas 70° C. and the heat-treatment was conducted at 170° C. Otherconditions were the same as in Comparative Example 1.

The ΔHu and ΔTm of the thus prepared heat-sensitive films were measured.Further, the thus obtained heat-sensitive films were laminated on, andadhered to a polyester gauze and was subjected to printing using theprinter, and character printing characteristics, paint-printingcharacteristics, sensitivity and withstand printing number wereevaluated as mentioned above. The results are shown in Table 1.

COMPARATIVE EXAMPLE 3

Polyethyleneterephthalate-isophthalate copolymer containing 25% byweight of isophthalate was blended in polyethyleneterephthalate resin inthe amount of 70% by weight, and the same procedure as in ComparativeExample 2 was repeated using this material to form a heat-sensitivefilm.

The ΔHu and ΔTm of the thus prepared heat-sensitive film was measured.Further, the thus obtained heat-sensitive film was laminated on, andadhered to a polyester gauze and was subjected to printing using theprinter, and character printing characteristics, paint-printingcharacteristics, sensitivity and withstand printing number wereevaluated as mentioned above. The results are shown in Table 1.

                                      TABLE 1-1                                   __________________________________________________________________________                  Characters Printing                                                    ΔHu                                                                         ΔTm          Unevenness                                      Example                                                                              (cal/g)                                                                           (°C.)                                                                     Clearness                                                                          Chipping                                                                           Thickness                                                                           of Thickness                                    __________________________________________________________________________    Comparative                                                                          13  40 A    ×                                                                            ×                                                                             ◯                                   Example 1                                                                     Example 1                                                                            11  50 A    Δ                                                                            Δ                                                                             ◯                                   Example 2                                                                            10  60 A    ◯                                                                      ◯                                                                       ◯                                   Example 3                                                                            7   80 A    ◯                                                                      ◯                                                                       ◯                                   Example 4                                                                            5   90 A    ◯                                                                      ◯                                                                       ◯                                   Example 5                                                                            3   100                                                                              B    ◯                                                                      Δ                                                                             ◯                                   Comparative                                                                          0   ∞                                                                          C    Δ                                                                            ×                                                                             ×                                         Example 2                                                                     Comparative                                                                          5   120                                                                              A    ◯                                                                      ×                                                                             ×                                         Example 3                                                                     __________________________________________________________________________

                                      TABLE 1-2                                   __________________________________________________________________________           Paint-Printing                 Withstand                               Example                                                                              Clearness                                                                          Size Correspondence                                                                      Light and Shade                                                                        Sensitivity                                                                         Printing Number                         __________________________________________________________________________    Comparative                                                                          ×                                                                            ×    ×   H    3000                                    Example 1                                                                     Example 1                                                                            Δ                                                                            Δ    Δ  3H    2900                                    Example 2                                                                            ◯                                                                      ◯                                                                            ◯                                                                          4H    2750                                    Example 3                                                                            ◯                                                                      ◯                                                                            ◯                                                                          5H    2700                                    Example 4                                                                            ◯                                                                      ◯                                                                            ◯                                                                          5H    2695                                    Example 5                                                                            ◯                                                                      ◯                                                                            ◯                                                                          5H    2300                                    Comparative                                                                          ×                                                                            ×    ◯                                                                          3H    1000                                    Example 2                                                                     Comparative                                                                          Δ                                                                            ×    ◯                                                                          3H    2000                                    Example 3                                                                     __________________________________________________________________________

As is apparent from Table 1, the biaxially stretched films of thepresent invention of which ΔHu is in the range of 3-11 cal/g and ofwhich ΔTm is in the range of 50°-100° C. are excellent in both characterprinting and paint-printing characteristics.

EXAMPLES 6-14

Ethyleneterephthalate-isophthalate copolymer (ethyleneisophthalatecontent of 12.5 mol %) with an intrinsic viscosity of 0.6 was blendedwith ethyleneterephthalate-isophthalate copolymer (ethyleneisophthalatecontent of 12.5 mol %) with an intrinsic viscosity of 0.7 containing2.0% by weight of SiO₂ particles with an average particle size of 0.3 μm(Example 6), 1.1 μm (Example 7) or 2.0 μm (Example 8) in the amount suchthat the SiO₂ content at the time of melt-extrusion is 0.15% by weight.

As to Examples 9-13, polyethyleneterephthalate with an intrinsicviscosity of 0.6 containing SiO₂ particles with an average particle sizeof 0.1 μm (Example 9), 0.8 μm (Example 10), 1.3 μm (Example 11), 1:1mixture of 2.0 μm and 3.5 μm (Example 12) or 1:1 mixture of 2.0 μm and4.0 μm was blended with the above-mentionedethyleneterephthalate-isophthalate copolymer used in Examples 6-8 in theamount such that the content of SiO₂ at the time of melt-extrusion was0.25% by weight.

Using these materials, biaxially stretched films with a thickness of 1.5μm were prepared as in Example 1.

The ΔHu, the ΔTm, the center line surface roughness, the maximumroughness and the number of projections were determined and thestretching property and the winding property were evaluated. Further,the thus obtained heat-sensitive films were laminated on, and adhered toa polyester gauze and was subjected to printing using the printer, andcharacter printing characteristics, paint-printing characteristics,sensitivity and withstand printing number were evaluated as mentionedabove. The results are shown in Table 2.

As is apparent from Table 2, by adopting the above-described specificsurface configuration, heat-sensitive films which are excellent not onlyin printing characteristics, sensitivity and withstand printing numberbut also in stretching property and winding property can be obtained.

                                      TABLE 2-1                                   __________________________________________________________________________                        Number of                                                                     Projections/mm.sup.2   Characters Printing                       ΔHu                                                                         ΔTm                                                                        Ra Rt 1 μm φ                                                                             Stretching                                                                          Winding                                                                            Clear-                                                                            Chip-                                                                             Thick-                                                                            Unevenness of          Example                                                                              (cal/g)                                                                           (°C.)                                                                     (μm)                                                                          (μm)                                                                          or larger                                                                           8-20 μm φ                                                                    Property                                                                            Property                                                                           ness                                                                              ping                                                                              ness                                                                              Thickness              __________________________________________________________________________    Example 6                                                                            6.9 86 0.05                                                                             1.32                                                                             5812  267   ◯                                                                       ◯                                                                      A   ◯                                                                     ◯                                                                     ◯          Example 7                                                                            6.7 85 0.10                                                                             2.09                                                                             5650  322   ◯                                                                       ⊚                                                                   A   ◯                                                                     ◯                                                                     ◯          Example 8                                                                            6.5 84 0.20                                                                             2.55                                                                             5950  545   ◯                                                                       ⊚                                                                   A   ◯                                                                     ◯                                                                     ◯          Example 9                                                                            7.0 86 0.08                                                                             0.5                                                                              6425   43   ◯                                                                       ◯                                                                      A   ◯                                                                     ◯                                                                     ◯          Example 10                                                                           7.4 88 0.10                                                                             0.8                                                                              6213   53   ◯                                                                       ⊚                                                                   A   ◯                                                                     ◯                                                                     ◯          Example 11                                                                           7.5 88 0.12                                                                             1.7                                                                              5900  101   ◯                                                                       ⊚                                                                   A   ◯                                                                     ◯                                                                     ◯          Comparative                                                                          7.3 87 0.19                                                                             3.3                                                                              5321  113   ◯                                                                       ⊚                                                                   A   ◯                                                                     ◯                                                                     ◯          Example 12                                                                    Comparative                                                                          7.1 86 0.20                                                                             4.0                                                                              5153  210   ◯                                                                       ⊚                                                                   A   ◯                                                                     ◯                                                                     ◯          Example 13                                                                    __________________________________________________________________________

                  TABLE 2-2                                                       ______________________________________                                               Paint-Printing                                                                          Size                  Withstand                                       Clear-  Corres-  Light and                                                                            Sensi-                                                                              Printing                               Example  ness    pondence Shade  tivity                                                                              Number                                 ______________________________________                                        Example 6                                                                              ◯                                                                         ◯                                                                          ◯                                                                        5H    2640                                   Example 7                                                                              ◯                                                                         ◯                                                                          ◯                                                                        5H    2600                                   Example 8                                                                              ◯                                                                         ◯                                                                          ◯                                                                        5H    2590                                   Example 9                                                                              ◯                                                                         ◯                                                                          ◯                                                                        5H    2690                                   Example 10                                                                             ◯                                                                         ◯                                                                          ◯                                                                        5H    2680                                   Example 11                                                                             ◯                                                                         ◯                                                                          ◯                                                                        5H    2550                                   Comparative                                                                            ◯                                                                         ◯                                                                          ◯                                                                        5H    2520                                   Example 12                                                                    Comparative                                                                            ◯                                                                         ◯                                                                          ◯                                                                        5H    2480                                   Example 13                                                                    ______________________________________                                    

EXAMPLES 14-18

To 100 parts by weight of ethyleneterephthalate-isophthalate copolymerwith an isophthalate content of 22.5 mol % (Example 14), 20 mol %(Example 15), 17.5 mol % (Example 16), 15 mol % (Example 17) and 2.5 mol% (Example 18), 0.51 parts by weight of carubauna wax was added. Eachmaterial had an intrinsic viscosity of 0.6. Each material was suppliedto an extruder and was melt-extruded through a T-die at 280° C. Themolten resins were cast onto a cooling drum with a temperature of 50° C.to form cast films. The films were stretched to 4.5 times the originallength at 70°-90° C. in the longitudinal direction. The films were thenstretched to three times the original length at 80° C. in transversedirection. The films were subsequently heat-treated in the stenter at150° C. for 5 seconds to obtain biaxially stretched films having athickness of 2.0 μ m.

The ΔHu, ΔTm and heat shrinkage of the thus obtained heat-sensitivefilms were measured. Further, the thus obtained heat-sensitive film waslaminated on, and adhered to a polyester gauze and was subjected toprinting using the printer, and character printing characteristics,paint-printing characteristics, sensitivity, withstand printing number,releasing property, adhesiveness, anti-curling property were evaluatedas mentioned above. The results are shown in Table 3.

As is apparent from Table 3, by incorporating the above-describedspecific wax in the heat-sensitive film of the present invention, theheat-sensitive films with especially excellent printing characteristicsand sensitivity can be prepared.

                                      TABLE 3-1                                   __________________________________________________________________________    ΔHu ΔTm                                                                        Heat Shrinkage                                                                        Releasing   Anti-Curling                                                                         Characters Printing                   Example                                                                             (cal/g)                                                                           (°C.)                                                                     (%)     Property                                                                           Adhesiveness                                                                         Property                                                                             Clearness                                                                          Unevenness of                    __________________________________________________________________________                                                 Thickness                        Example 14                                                                          3      10      Δ                                                                            ◯                                                                        ◯                                                                        B    Δ                          Example 15                                                                          5      10      ◯                                                                      ◯                                                                        ◯                                                                        A    ◯                    Example 16                                                                          7      10      ◯                                                                      ◯                                                                        ◯                                                                        A    ◯                    Example 17                                                                          10     10      ◯                                                                      ◯                                                                        ◯                                                                        A    ◯                    Example 18                                                                          11     10      ◯                                                                      ◯                                                                        ◯                                                                        A    ◯                    __________________________________________________________________________

                  TABLE 3-2                                                       ______________________________________                                               Paint-Printing                                                                          Size                  Withstand                                       Clear-  Corres-  Light and                                                                            Sensi-                                                                              Printing                               Example  ness    pondence Shade  tivity                                                                              Number                                 ______________________________________                                        Example 14                                                                             ◯                                                                         ◯                                                                          Δ                                                                              4H    3000                                   Example 15                                                                             ◯                                                                         ◯                                                                          ◯                                                                        6H    3500                                   Example 16                                                                             ◯                                                                         ◯                                                                          ◯                                                                        6H    4000                                   Example 17                                                                             ◯                                                                         ◯                                                                          ◯                                                                        6H    3900                                   Example 18                                                                             Δ ◯                                                                          ◯                                                                        4H    4100                                   ______________________________________                                    

EXAMPLES 19-22

Polyester copolymer prepared from an acid component of terephthalicacid/isophthalic acid=85 mol %/15 mol % and glycol component ofethyleneglycol was dried and was supplied to an extruder. The copolymerwas melt-extruded at 290° C., and was cast onto a cooling drum with atemperature of 40° C. while applying a static voltage. Then the thusobtained film was stretched to 3.8 times the original length at 80° C.in the longitudinal direction. On the thus prepared uniaxially stretchedfilm, an aqueous solution containing 8% by weight of a mixture of apolyester copolymer I and an organopolysiloxane II with a mixing ratioshown in Table 4 was applied. The film was then stretched to 3.5 timesthe original length in the transverse direction while drying the coatedsolution, and was then heatset at 150° C. with 2% relaxation.

On reverse side of the thus obtained heat-sensitive film having a nonhot-sticking layer thereon, vinyl acetate-based adhesive was appliedusing a wire bar and a porous tissue paper with a thickness of 40 μm wassuperposed thereon to wet-laminate the same and the resulting laminatewas dried at 100° C. to adhere the tissue paper.

The thus prepared heat-sensitive mimeograph stencil was subjected toprinting and the various characteristics shown in Table 4 wereevaluated.

                                      TABLE 4-1                                   __________________________________________________________________________                 Composition of Non-                                                                           Thickness of              Surface Wetting        ΔHu ΔTm                                                                        Hot Sticking Layer                                                                            Non-Hot Sticking                                                                       Anti-Sticking                                                                            State of                                                                            Tension                Example                                                                             (cal/g)                                                                           (°C.)                                                                     A  B  Weight Ratio A/B                                                                        Layer (μm)                                                                          Property                                                                             Noise                                                                             Perforation                                                                         Front/Reverse          __________________________________________________________________________    Example 19                                                                          5   90 I  II 0.05      0.01     ◯                                                                        ◯                                                                     ◯                                                                       36/40                  Example 20                                                                          5   90 I  II 0.25      0.01     ⊚                                                                     ◯                                                                     ◯                                                                       36/40                  Example 21                                                                          5   90 I  II 0.5       0.01     ⊚                                                                     ◯                                                                     ◯                                                                       36/39                  Example 22                                                                          5   90 I  II 1         0.01     ⊚                                                                     ◯                                                                     ◯                                                                       36/38                  __________________________________________________________________________

                                      TABLE 4-2                                   __________________________________________________________________________    Characters Printing                                                                                 Unevenness of                                                                         Paint-Printing                                  Example                                                                             Clearness                                                                          Chipping                                                                           Thickness                                                                           Thickness                                                                             Clearness                                                                          Size Correspondence                                                                      Light and                       __________________________________________________________________________                                                  Shade                           Example 19                                                                          B    ◯                                                                      ◯                                                                       ◯                                                                         ◯                                                                      ◯                                                                            ◯                   Example 20                                                                          B    ◯                                                                      ◯                                                                       ◯                                                                         ◯                                                                      ◯                                                                            ◯                   Exampel 21                                                                          B    ◯                                                                      ◯                                                                       ◯                                                                         ◯                                                                      ◯                                                                            ◯                   Example 22                                                                          B    ◯                                                                      ◯                                                                       ◯                                                                         ◯                                                                      ◯                                                                            ◯                   __________________________________________________________________________

                  TABLE 4-3                                                       ______________________________________                                                          Withstand    Sticking to Original                           Example Sensitivity                                                                             Printing Number                                                                            Copy (Manuscript)                              ______________________________________                                        Example 19                                                                            5H        2300         ◯                                  Example 20                                                                            5H        2350         ◯                                  Example 21                                                                            5H        2380         ◯                                  Example 22                                                                            5H        2380         ◯                                  ______________________________________                                    

As can be seen from Table 4, by using the heat-sensitive mimeographstencil of the present invention which has a non hot-sticking layer, notonly excellent printing characteristics but also excellent anti-stickingproperty can be obtained. Particularly, when the composition of the nohot-sticking layer (weight ratio of B/A) is in the range of 0.1 to 0.7,actually 0.25 or 0.5 in the examples, the balance of theanti-transcription property (surface wetting tension of the reverseside) and the anti-sticking property are good.

The polyester copolymer I, cross-linking agent, organopolysiloxane IIwhich were used in Examples 19-22 were as follows: Polyester copolymerI: Polyester copolymer prepared by polycondensation of a dicarboxylicacid component of terephthalic acid/isophthalic acid (50/50 mol %) and aglycol component of ethyleneglycol/neopentylglycol (45/55 mol %) with amolecular weight of about 20,000, glass transition temperature of 67° C.and intrinsic viscosity of 0.53. Cross-linking Agent: "Coronate L"(tradename of Nippon Urethane Co., Ltd.) which is an adduct of 1 mole oftrimethylolpropane and 3 moles of 2,4-tolylenediisocyanate. Thecross-linking agent was added in the amount of 20 parts in terms ofsolid contents. Organopolysiloxane: Epoxypolyether-modified silicone oil(trade name "Toray Silicone SF8421" manufactured by Toray SiliconeInc.).

We claim:
 1. A film for a heat-sensitive mimeograph stencil comprising apolyester-based biaxially stretched film which has an energy of crystalfusion ΔHu of 3-11 cal/g and has a difference ΔTm between the crystalfusion-terminating temperature and the crystal fusion-startingtemperature of 50° C. to 100° c.
 2. The film of claim 1, wherein thesurface of the film has a center line average roughness Ra of 0.05-0.3μm, maximum roughness Rt of 0.5-4.0 μm, 2,000-10,000 mm² of projectionswith a diameter of 1 μm or more and 20-1,000/mm² of projection with adiameter of 8-20 μm.
 3. The film of claim 2, further comprising at leastone kind of particle made of a material selected from the groupconsisting of oxides and inorganic salts of an element belonging to theIIA group, IIIB group, IVA group and IVB group in the periodic table. 4.The film of claim 3, wherein the content of the particles is 0.05-2% byweight.
 5. The film of claim 1, further comprising at least one higheraliphatic substance of which a major component is C₁₀ -C₃₃ higheraliphatic monocarboxylic acid or an ester thereof.
 6. The film of claim5, wherein the content of the higher aliphatic substance is 0.005-5% byweight based on the weight of the polyester constituting the film. 7.The film of claim 1, wherein the energy of crystal fusion ΔHu is 5-10cal/g.
 8. A heat-sensitive mimeograph stencil comprising a poroussupport and the film of claim 1 laminated on the porous support.
 9. Thestencil of claim 8, further comprising a non hot-sticking layer on thesurface of the film which surface is other than the surface contactingthe porous support.
 10. The stencil of claim 9, wherein the nonhot-sticking layer comprises as a major component at least one materialsselected from the group consisting of thermosetting silicone resins,thermoplastic silicone resins, epoxy resins, melamine resins, phenolresins, thermosetting acrylic resins, polyimide resins, metal salts ofaliphatic acids, phosphoric acid esters, supercooling substance,fluorine resins, perfluoroacrylic resins, vinyl chloride resins andvinilidene chloride resins.
 11. The stencil of claim 9, wherein the nonhot-sticking layer consists essentially of a mixture of polyestercopolymer (A) and organopolysiloxane (B), the weight ratio (B/A) of themixture being 0.01 to
 8. 12. The stencil of claim 12, wherein the nonhot-sticking layer comprises at least 10% by weight of cured materialconsisting essentially of an urethane prepolymer having a principalchain of an organopolysiloxane and containing a free isocyanate group asterminal group and/or pendant group.
 13. The stencil of claim 7, whereinthe non hot-sticking layer comprises cured material consistingessentially of a mixture of an urethane prepolymer (A) having aprincipal chain of an organopolysiloxane and containing a freeisocyanate group as terminal group and/or pendant group, and activehydrogen-containing polymer (B) with the weight ratio of (A)/(B) of10/90 to 90/10.